Modern gas turbines often operate at extremely high temperatures. The effect of temperature on the turbine blades and/or stator vanes can be detrimental to the efficient operation of the turbine and can, in extreme circumstances, lead to distortion and possible failure of the blade or vane. In order to overcome this risk, high temperature turbines may include hollow blades or vanes incorporating so-called impingement tubes for cooling purposes.
These so-called impingement tubes are hollow tubes that run radially within the blades or vanes. Air is forced into and along these tubes and emerges through suitable apertures into a void between the tubes and a interior surfaces of the hollow blades or vanes. This creates an internal air flow to cool the blade or vane.
Normally, blades and vanes are made by casting having hollow structures. Impingement tubes may be inserted into the hollow structure from one or other end and usually welded with the hollow structure to fix them in place. Chordal ribs are also often cast inside the blades, mainly to direct coolant and to provide a greater cooling surface area. These ribs, or specially cast ribs, may serve as location spacers for the impingement tubes, so as to create the necessary internal space for the cooling air.
Problems arise with fitting impingement tubes into the blades or vanes. Aerofoil sections of the blades or vanes may be extremely complicated. Hollow aerofoils may feature multidirectional curvature (complex shapes having 3-dimensional curvature) to improve an aerodynamic efficiency of the aerofoil, and hence increasing efficiency of the gas turbine. The amount of curvature and twist permitted on the aerofoil is limited by a need for the impingement tube to slide in from one end of the aerofoil.
Several techniques for enabling an impingement tube to be fitted inside such a hollow turbine blade or vane are known. U.S. Pat. No. 7,056,083 B2 discloses a turbine blade or vane with an impingement tube for cooling purposes located generally in a radial direction within the hollow blade or vane aerofoil. The impingement tube comprises two parts extending into the hollow aerofoil from opposite radial ends thereof and locating against a specially formed rib which extends generally chord wise around a leading edge of the aerofoil. The impingement tube is assembled from both ends of the hollow aerofoil and located against the formed rib approximately half way between the apertures of a cavity.
U.S. Pat. No. 4,798,515 A discloses a cooling arrangement for stator vanes for a turbo machine. Inside a cavity of the stator vane two impingement cooling inserts are arranged. They are brazed or force fitted via flared resilient portions of the inserts into inlet apertures of trunnions of the vane. The two impingement cooling inserts are inserted into the cavity from opposite ends of the vane. For connecting the two impingement cooling inserts to one another a positioning pin is provided at the impingement cooling insert which interacts with a positioning pin receptacle at the impingement cooling insert.
In U.S. Pat. No. 6,742,984 B1 a gas turbine having inserts for impingement-cooling of walls of a nozzle vane is shown. Each insert has two parts which are inserted successively inside a cavity of the vane so that they are arranged in the cavity at a same axial height from a leading to a trailing edge. The inserts are secured into position in the cavity by a welding or brazing operation. A leg section of each part of an insert extends in radial direction of the vane. Supporting rods, which extend perpendicular to the radial direction, are arranged between the leg sections to space them apart from one another. Moreover, these supporting rods are provided for maintaining standoffs at outer walls of the leg sections engaged against inner wall surfaces of the nozzle vane walls.
EP 1 626 162 A1 describes a vane assembly with a vane used in a gas turbine. A first and a second baffle of a baffle assembly are inserted into a cavity of the vane from opposite ends of the vane so that they are arranged in span wise direction radially one over the other. Further, the baffles are fixed to one another radially and inside the cavity by means of a fastener, which applies a spanwisely directed tensile load to the vane.
It is a first objective of the present invention to provide a method for assembling an impingement tube in a hollow aerofoil of an aerofoil-shaped gas turbine component such as gas turbine rotor blade and stator vane which the above-mentioned shortcomings can be mitigated, and especially a more aerodynamic efficient aerofoil and gas turbine component is facilitated.
It is a second objective of the invention to provide an advantageous aerofoil-shaped gas turbine component such as a gas turbine rotor blade and a stator vane. A third objective of the invention is to provide an advantageous impingement tube used in such a component for cooling purposes.